Background. There are conflicting reports about the importance of the renin-angiotensin system (RAS) on erythropoietin (Epo) sensitivity in haemodialysis patients, but the role of gender has not been studied specifically. The hypothesis underlying this study is that Epo resistance associated with RAS blockade (RASB) is specific to men and related to drug-induced lowering of circulating testosterone. Methods. Men and women undergoing chronic haemodialysis were divided into groups according to whether or not they were receiving RASB. Serum was collected pre-dialysis for determination of free testosterone levels by enzyme immunoassay. Routine laboratory data and Epo doses were collated and analysed for the 3 month period prior to the measurement of the hormone level. Results. Control women required more Epo than control men (P ¼ 0.002), but the Epo doses between men and women with RASB were similar. Men with RASB required more Epo than control men (P ¼ 0.002), but RASB had no effect on Epo requirements in women. There was a significant relationship between age and testosterone levels in control men (P ¼ 0.01) that was not present in men taking RASB. RASB was associated with lower levels of serum testosterone in men <60 years old (P ¼ 0.02), but had no effect on serum testosterone levels in older men or women. Multiple regression analysis demonstrated that serum testosterone negatively correlated with Epo dose (P ¼ 0.045) when all groups of patients were considered together. Conclusions. These data suggest that androgens may participate in Epo resistance associated with RASB in patients on haemodialysis, and that the effect is related to both gender and age.

Background The regulation and control of pressure stimuli is useful for many studies of pain and nociception especially those in the visceral pain field. In many in vivo experiments, distinct air and liquid stimuli at varying pressures are delivered to hollow organs such as the bladder, vagina, and colon. These stimuli are coupled with behavioral, molecular, or physiological read-outs of the response to the stimulus. Care must be taken to deliver precise timed stimuli during experimentation. For example, stimuli signals can be used online to precisely time-lock the stimulus with a physiological output. Such precision requires the development of specialized hardware to control the stimulus (e.g., air) while providing a precise read-out of pressure and stimulus signal markers. Methods In this study, we designed a timed pressure regulator [termed visceral pressure stimulator (VPS)] to control air flow, measure pressure (in mmHg), and send stimuli markers to online software. The device was built using a simple circuit and primarily off-the-shelf parts. A separate custom inline analog-to-digital pressure converter was used to validate the real pressure output of the VPS. Results Using commercial physiological software (Spike2, CED), we were able to measure mouse bladder pressure continuously during delivery of unique air stimulus trials in a mouse while simultaneously recording an electromyogram (EMG) of the overlying abdominal muscles. Conclusions This device will be useful for those who need to (1) deliver distinct pressure stimuli while (2) measuring the pressure in real-time and (3) monitoring stimulus on–off using physiological software.